Compressor regulator



No'v. 7, 1939.

A` o. CARPENTER 2,178,660

COMPRESS 0R REGULATOR I I `Filed Dec. 24, 1957 2 sheets-sheet 1 HISATTORNEY.

Nom 7, 1939. A. o. CARPENTER 2,178,660

COMPRESSOR REGULATOR Filed Dec. 24, 1937 2 sheets-sheet 2 .far

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` INVENTOR Wlan ayvmfei@ BYMf/g HIS ATTORNEY Patented Nov. 7, 1939 lPATENT OFFICE' 2L178,660 CONIPRESSOR REGULATOR Allan 0. Carpenter,Corning,

any, Jersey City,

Ingersoll-Rand Comp N. Y., assignor to N. J., a

corporation of New Jersey Application December l Claims.

This -invention relates to regulators for motor driven uid compressors,and more particularly to a regulator wherein the speed of the motor isoperated at either maximum speed or minimum 5 speed in accordance withthe output of the compressor.

A motor driven unit of this sort comprises a m'd compressor driven-by amotor or engine, such as an internal combustion motor or a steam engine,and a receiver tank to receive and store the fluid under pressuredischarged by the compresser. In the operation of the unit, thedischarge of iluid to the receiver continues until the pressure thereinreaches a predetermined l5. amount, whereupon, a device provided on thecompressor operates to prevent further discharge of fluid to thereceiver tank (commonly termed unloading) and, at the same time,decelerates the compressor driving motor to its minimum,

0 or idling, speed. The compressor then continues to operate in thismanner until the pressure in the receiver tank falls to a predeterminedmini,- mum point and then the device operates to permit the compressorto again discharge fluid to 25 the receiver tank (commonly termedreloading"), and to accelerate the motor to its maximum operating speed.

With this mode of operation the compressor, under light loads, williiuctuate rapidly between 3@ its minimum, or idling, speed and itsmaximum speed, resulting in ineicient and ineconomicalv operation oftheunit.

It is, accordingly, an object of the present invention, to provide ameans whereby a motor 35 driven compressor unit may reload while themotoris operating at its minimum speed.

It is a further object to provide means whereby, under light loads, itis impossible to reload the compressor at the maximum motor speed un- 40til a predetermined minimum discharge pressure of the compressor isreached.

A still further object is to provide means whereby the motor can notaccelerate to its maximum speed to reload the compressor, under 45 lightloads, until a predetermined minimum pressure is reached in the receiverand then only after a predetermined time delay.

It is a still further object to provide a device whereby resumption ofmaximum motor speed, after reloading, is prevented under light loads .Yand permitted when reloading occurs under heavy loads..

Another object is to provide a de'dce for con- 55 Atrolling the speedsetting of the governor' in action engine 'l directly connected to 24,1937, Serial N0. 181,656

cordance with variations in the discharge pressure of the compressor. ix

Another object is to provide a regulating device varying in accordancewith the discharge pressure of the compressor whereby, on the oc- 5currence of a predetermined high discharge pressure, the motor speed isreduced from the maximum speed to the minimum speed; of a predeterminedmaximum pressure, the compressor unloads; of a predetermined lowpressure, the compressor reloads; and of a predetermined minimumpressure, the motor accelerates from the minimum motor speed to themaximum motor speed.

These and other objects will be -readily apparent from the followingspecication oi which the drawings form a part and in which y Figure 1 isa view partly in elevation and partly in section illustrating vtheapplication of the present invention to a compressor unit, and in whichthe view cf the governor is increased in size in order to bring out thedetails more clearly.

Figure 2 illustrates in section the loading device shown in Fig. 1, andFigure 3 is a view partly in elevation and partly in section of part ofthe governor controlling device constructed in accordance with theprinciples of this invention.

It will be noted by referring to Fig. 1 that the compressor unitconsists of a fluid compressor I mounted on a frame 3 supported bywheels 5., The frame 3 also supports an internal combusdrive the uidcompressor I. Fluid tobe compressed by the compressor I is supplied bythe inlet conduit 9 and the conduit II- delivers the compressed fluiddischarged from the compressor to the receiver tank I3. Y The inlet'conduit 9 contains a means to unload and reload I5 which is illustratedin detail in Fig. 2. This device consists of a casing I1 connected tothe conduit 9 at its upper end and to the compressor I at its lower end.The casing is so designed that aportion of the wall extends within theouter walls thereof and forms valve guides I9 for the balancedcylindrical reciprocating valve 2|. A plate 23 closes an opening 24- inthe side wall of the casing I1 and is provided with a recess 26 inwhichfrests a spring 25, normally urging the cylindrical valve 2|towards Vthe right or open position. With the valve in the open positionshown in Fig. 2- it is readily apparent that uid may enterl through theconduit 9, pass aroundthe valve 2l and ow into the compressor.

, piston chamber and to transmit its motion to the valve 2| by bearingon the pin 33 formed as an integral part of the cylindrical valve 2|.

When the pressure exerted by the piston 29 on the valve 2| is suilcientto overcome the force of the spring 25, the cylindrical valve 2| will bemoved away from its seat 3|. Movement of the valve from its seat willshut cif communication between the inlet conduit 9 and the compressor Iwhen the ribs 35 are moved into alignment with the walls of the casingI1, which form the guides I9 for the valve 2|.

At one side o1 the piston chamberl 21 and communiting therewith is apressure operated auxauxiliary valve iliary valve, generally designatedas 35. This valve serves to control the admission of pressure uid to thepiston chamber, and thus themove-4 ment of the piston against the forceof the spring 25. The auxiliary valve 36 comprises a valve body 31communicating directly with the receiver tank I3 through the conduit 39.In order to prevent continuous communication between the receiver tankand the piston chamber 21 an proper 4| is normally pressed on the seat43 by the member 45. As is apparent from the ligure, the member 45transmits the pressure of thespring 41, which is compressed between thismember and the bushing 49. Y

In the event that the pressure in the receiver tankis sumcient to movethe auxiliary valve proper 4| from its seat 43 against the compressiveVforce of tt spring 41, a second seat 5| is provided by a bushing 53 inthe auxiliary valve body 31 and providing the valve 4| with an appro,Vpriate face to rest on this seat. By adjusting the bushing 49, thecompression of the spring 41 may be or decreased, and the pressure atwhich the valve 4| willleave its seat 43 and seek its seat 5| may thusbe predetermined, and also theprsure 'at whichthe valve 4| returns toits seat 43.

From the above description it will be seen that when the prmure in thereceiverA reaches a'predetermined point, which is suflcient to overcomethe compressive force of the spring 41, the valve 4| Awill open, therebypermitting fluid to Ilowf past the valve seat 43, through the channelV55, into the piston chamber 21, and cause the piston to Push the tion.The pressure which is necessary to 'open the valve 4| is greater Ythanthat required to maintain the valve open, since the eiiective pressurearea ct the valve is increased by the portionY the valve which seats ofthe diametrlcal area of onthe seat 43 when the valve is closed.

' VVthat the spring 41 can return Howevenwhen the pressure fallssuiiiciently so seat 43, the-tluid'trapped in the chamber 21 must beallowed to escape. Thisvis-'accomplished by permitting the uidtc owthrough the channel 55, by-the seat-5L and through a central opening 51,in the bushing 49, surrounding the member 4l to the atmosphere. Whenthefluid has been exhausted from the piston chamber, the com-- preasiveforce of thev spring will move 'the cylindrical valve 2| from its closedposition to its open position and return the valve 2| to its seat 3|. s

reciprocate in the i bear against a cylindrical valve to its closedp0si- -against a hooked lever the valve 4| to itsA .By way ofsummarizing the action of. this device, it may be said that'when thepressure inthe receiver tank reaches a predetermined point the auxiliaryvalve opens and permits the fluid pressure to close the cylindricalvalve tof unload the machine. When the pressure has fallen to apredetermined low point, the auxiliary valve closes, the fluid pressureescapes from the piston chamber and the cylindrical valve opens to againreload thecompressor.

With reference to Fig. 1 `the speed oi the internal combustion motor iscontrolledby a governor, generally indicated at 59, which consists of ashaft 6| directly connected to the shaft (not shown) of the engine. Agear 63 secured to a ange on the shaft 6| is provided with ears 65 onwhich are fulcrumed weights 61. gine rotates, the centrifugal forcemoves the weights away from the shaft 6| in accordance with the speed ofthe motor, until they reach their' outermost position at which time theyact to prevent further increase in the speed of the motor. Rollers 69mounted on the weights 61 plate sion on the shaft 6|. Hence, as theweights move outwardly vthe governor spring 891s compressed and themotion of VthepIate 1| is transmitted, through an anti-friction bearing13, to a plate 15, formed integrally with the pin 11 coaxial with andslidably mounted on the shaft 6|.

The plate 15 is provided-with a clevis 19 surrounding and pinned tolever 9| fulcrumed on theW ment of the weights 61 inwardly toward theshaft 6|, moves the plate 1.| in the same direction, thus pivoting thelever 8| about its iul'crum 83 and moving the butteriyvalve 81 by meansof the rod 95 toward the open position to accelerate the Conversely,Awhen gine is increased, the lever 9| and rod |15,v under the influenceof the spring 99, move the butterily valve in the opposite direction todecrease the fuelsupply to the motor.

As is customary in centrifugal governors, the weights 61 are resilientlyheld in their retracted position and to this end a spring 89 isprovided. 'I'his spring is housed in a casing 9| secured to the frame ofthe motor and having a bore 93 extending therethrough. The borecommunicates at one end with a recess 95 in which the spring iscontained and has a plunger 91 extending therethrough and provided witha flange against which one end of the spring 89 rests. The other end ofthe spring pushes a member 99 against the projection ||l| formed on thelever 8|.

'I'he external end of the plunger 91 bears |93, fulcrumed on the 9|, andis adapted to transmit forceto The speed setting of the by the amount ofthe casing compress the spring 99. governor is determined force theweights 61 must exert to mcve the plate Hence, if the hooked leverforces the plunger 91 to compress the spring to the limit, a muchgreater speed of the motor'willbe necessary in order that thecentrifugal force of the weights 6l shall be suilcient to move -theplate 'Il' outwardly from the shaft against the resistance oi'the'spring I9. Under these conditions, consequently, the plate 1|, thelever 3|. and rod 95,l wil not be moved to throttle and 1| surroundingan exten-v the speed of the encompression When the endecrease thespeedof the motor until the speed of the motor exceeds the maximumspeed atwhich it is desired to operate the motor.

, against the compression the conduit 33.

valve itil will remain Conversely, if the hooked lever |03 is moved :othat the spring 89 may expand, move the ilunger 91 to the left, theplate 1| may be moved iut from the shaft 6| by the weights 61 when ;hemotor is running at a much slower rate. The result is that the motorwill operate at a greatly reduced speed and a slight increase in speedwill cause the weights to move the plate 1| further away from the shaftthereby throttling the motor intake and decreasing the speed to thedesired Thus, if the position of the hooked lever |03 is regulated, thespeed setting of the governor may be regulated, and or that reason apressure responsive device having two control positions is connected tothis lever by the tie-rod |05.

The details of the regulating mechanism are best illustrated byreference to Fig. 3. 'The reguiating mechanism consists of a chamberedcasing im, having a bore |09 communicating with the piston chamber lil.The piston`||3 in the chamber is secured to a shaft ||5 extendingthrough the bore |09 and connected to the lever M1 fulcrumed on theframe of the motor at lld.- At the end of the lever opposite to that onwhich the shaft H5 is secured, is the tie-rod |05 which connects withthe hooked lever |03. In one end of the chamber Hl is a recess |2l inwhich.v rests a spring |23 bearing against the piston M3 and normallyurging it toward the right.

The end of the chambered casing H01 is closed by a plate E25 suitablysecured thereto. A conduit i2i extends through this plate chamber llland bears against the piston H3. Slots 629 are provided in the end ofthe conduit which hears againstthe piston to provide a large' Thisconduit opening into the piston chamber. communicates with a meansresponsive to the discharge pressure such as an .auxiliary r`valvemechanism, generally indicated at |3l, which is similar in constructionto the auxiliary, valve mechanism i described in connection with theunloading and reloading device, V.and also communicates with thereceiver Since the structural features of the auxiliary valve mechanismauxiliary valve mechanism 3E, described in connection with the unloadingand reloading device, the same numerals with a numeral t added as `as'nx are used toindicate'sirnilar parts, and description or theauxiliary valve |36 Will be dispensed with. Y Likewise the operation ofthis valve is the same as the operation of the previously describedvalve, except for the fact that diierent receiver pressures are employedto open and close the valve. The regulation ofthe pressures, of course,being accomplished by varying the compressive torce o the spring Bi.

During the operation of the compressor the closed during the initialperiod of loading the receiver. However, when the pressure inthereceiver tank rises to a point where it isrsuiiicient to move the valve4| Il'irom its seat @3i against the compression of the spring fili, uuidwill now from the receiver tank past the seat 613i, into the conduit|21, and escape into the piston chamber il! thereby exerting pressure onthe piston l I3 and moving the piston of springy |23 toward the left.The movement of the piston is transmitted to the lever ill by the shaftl|5 and consequent movement of the tie-rod |05 will move piston chamber,the piston into the piston tank by means o iti are similar to those oftheV upon the will of the operator who the hooked lever away from theplunger 91 and permit ,the spring 8B to expand.

Releasing the compressive force on the spring 89 permits the lug l0bearing' against the member 99, to move further to the left with theresult 5 that the butterfly valve 81 closes. The motor will then operateat its minimum speed as was previously explained: This state continuesso long as the valve 4|| is resting on its seat 5H and allowing thepassage of iluid from the receiver tank 410 by the seat 43|.

When the pressure in the receiver tank begins to fall the valve willremain open until the pressure on the valve dll is no longer sufcient toovercome the compressive force exerted by the spring 41|.`

` The pressure required to hold the valve open is considerably less thanthe pressure required to open the valve. This will be readily apparentwhen it'is noted that the effective pressure area.

is increased to the total diametrical area of the 20 valve 4| l, as waspointed out in the description of valve 4| in the auxiliary valve 36.Upon the closing of the valve 41|, shutting off the flow vof fluid underpressure from the receiver to the move from its left-hand position backto the normal unactuated chamber. This is due to the fact that uid underpressure remains in the chamber when the valve 4H closes and,accordingly an escape for the uid 30 in the chamber is provided,similar-to the escape provided with the unloading and-reloading device36.

The path for the quently, through the |21, past the seat 5| i, throughthe channel 51|, to the atmosphere. With this arrangement the pistonchamber is normally open to atmospheric pressure and it is only when thepredetermined high pressure occurs iluid is admitted therefrom to thepiston chamber, and at that time the atmospheric vent is closed by thevalve 4H as it rests on the seat 5| l.

In the operation of the entire regulating means escape of `uid is,consethe predetermined high presure at which the aux- 45 iliary valve|3l opens is slightly less than the maximum allowable pressure at whichthe auxiliary valve 35 opens. For example, the valve 13B may open at 100pounds per square inch and the valve 36 at 105 pounds per square inch.The 50 regulation of these pressures, of course, depends may vary thecompressive force of the springs 4l or Ml in the manner described. Asthe opening pressures for the respective valves are different, inaccordance `with this invention the corresponding closing pressures areadjusted to be different. Thus the corresponding closing predeterminedlow pressure for the auxiliary valve 3B may be 85 pounds per squareinch, whereas the corresponding closing, 6G ,or predetermined minimum,pressure for the auxiliary valve |3| may be`80 pounds per square inch.In general the operation oi the unit is as follows: When the machine isstarted, assuming no pressure at the receiver, both oi the auxiliaryvalves 3E and |.3I are closed leaving the unloader valve 2| in its openposition and the piston H3 in its right-hand position, corresponding tothe vmaximum speed setting of the motor governor.

When the pressure builds up to the pounds 70 per square inch, the valveMl opens, the piston H3 movesto its left-hand position and changes thegovernor speed setting to the minimum speed.

If the load is constanh'thecompressor will then operate to supply vthenecessary require- 75 does not immediately 25 position at the right ofthe slots |29, into the conduit 35 in the receiver tant. that 40`-pounds per square inch, the valve ments at the minimum speed of themotor. It the pressure should continue to build up in the receiver tothe maximum allowable pressure, 105 pounds per square inch, the valve 4|operates to close the unloading valve 2| and thereby prevents furtherdischarge of air to the receiver. It the load now increases, thepressure in the receiver tank will fall and when itl reaches 85 y4I theunloading valve 2| opens again permitting the discharge of air from thecompressor to the receiver. So long as the load does not increase to thepoint where the pressure in the receiver tank falls to 80 pounds persquare inch, the valve 4H remains open and the machine will continue tooperate at minimum speed. Should the load increase, however, and thepressure fall to the minimum allowable pressure of pounds per squareinch, the valve 4H will close, permitting the fluid in the chamber IIIto escape to atmosphere and the piston tomove to its righthand positionthus causing the motor again to accelerate to its maximum speed.

It is thus apparent that during the operation of the compressor theregulating means will oper ate to maintain the motor running at minimumspeed so long as the load does not require the motor to run at maximumspeed, and the cycle of operation will be similar to that described.

It is understood that the described is a preferred embodiment of theinvention and that many changes which do not depart from the'scope andspirit of the invention will occur to those skilled inthe art.

I claim:

1. In a regulator for a motor driven fluid compressor having a speedgovernor, a compressor discharge controlled pressure responsive .devicefor controlling the speed setting of the governor having two controlpositions, means to unload the compressor at a predetermined maximumdischarge pressure and to reload the compressor at a predetermined lowdischarge pressure, and means responsive to a predetermined highdischarge pressure intermediate the maximum and low discharge pressuresto enable the discharge pressure to set and maintain. the pressureresponsive device in one control position 'until a predeterminedminimumdischarge pressure less than said low discharge pressure is reached.

2. In a regulator for a motor driven luid compressor having a fluidreceiver tank and a speed governor, a pressure device for controllingthe speed setting of the governor actuated by .the fluid pressure in thereceiver tank, means to unload the com pressor ,at a predeterminedmaximum pressure in the receiver-tank and to reload th compressor at apredetermined low pressure in the receiver tank, means responsive to apredetermined high pressure intermediate the maximum and low pressuresin the receiver tank to admit fluid therefrom to the pressure device andresponsive to a predetermined minimum pressure less than the lowpressure in the receiver tank to prevent admission of fluid therefrom tothe pressure device, and means to regulate the predetermined high andpredetermined minimum pressures. f

3. 1n a regulator for a motor driven iluid compressor having a iluidreceiver tank and a speed governor, a pressure operated device forcontrolling the speed setting of the governor in accordance with thefluid pressure in the receiver tank having a maximum speed settingposition and a minimum speed setting position, means to uncloses andconstruction i above mediate said maximum load the compressor at apredetermined maximum pressure in the receiver tank and to reload thecompressor at a predetermined low pressure in the receiver tank, meansnormally preventing admission of iluid from` the receiver tank tothepressure responsive device to enable said pressure responsive device toremain at its maximum speed setting position and adapted to admit fluidto said pressure responsive device when a predetermined high pressureintermediate the predetermined maximum and low pressures is reacheduntil a predetermined minimum pressure less than the predetermined lowpressure is reachedv to change said pressure responsive device to andmaintain it at the minimum speed setting position.

4. In a regulator for amotor driven fluid compressor adapted todischarge fluid under pressure to a receiving means and having a speedcontrol governor, means to unload the compressor at a predeterminedmaximum discharge pressure and to reload the compressor at apredetermined low discharge pressure, pressure means in communicationwith the receiving means to control the speed setting of the governor,and means normally preventing communication between said pressure meansand the receiving means adapted to permit communication with thepressure in the receiving means is within a predetermined range after apredetermined high pressure interand low pressures has been reached.

5. A regulator for a motor driven fluid compressor having a governor, apressure responsive device for controlling the speedsetting of thegovernor in accordance with variations in the discharge pressure of thecompressor having two control positions, means to unload the compressorat a predetermined maximum pressure and to reload the compressor at`apredetermined low discharge pressure,v adjustable means to predeterminethe discharge pressures atwhich the last said means operates, meansl torender the pressure responsive device operative to assume onel controlposition at a' predetermined high pressure intermediate said pressuresand to assume the other control position when a predetermined minimumpressure less than said low pressure is reached. and ad- `iustable meansto regulate the pressures at which the last said means operates.'

6. A regulator for a motor driven iluid compressor having a governor, apressure responsive device for controlling the speed setting of thegovernor in accordance with variations in the discharge pressure of thecompressor having two pressure and to reload the compressor at a pre'determined lowl discharge pressure, adjustable means to` predeterminethe pressure at which the last said means operates, and means to renderthe pressure responsive device operative torassume one control positionat a predetermined high discharge pressure intermediate saidpredetermined maximum and predetermined low discharge pressures and toassume the other control position at a predetermined minimum dischargepressure less than said predetermined low dischargeipressure, means topredetermine the pressures at which the last said means operates, andmeans associated with the last said means to normally subject thepressure responsive device to atmospheric pressure.

7. A regulator for a motor driven iuid compressor having a governor, apressure responsive device for controlling the speed setting of thegovernor in accordance with variations in the discharge pressure of thecompressor having a maximum speed setting position and a minimum speedsetting position and normally maintaining the governor at maximum speedsetting, means to unload the compressor at a predetermined maximumdischarge pressure and to reload the compressor at a predetermined lowdischarge pressure, means to render the pressure responsive deviceoperative to change the governor to the minimum speed setting at apredetermined high pressure intermediate said predetermined maximum andlow discharge pressures and maintaining that speed setting within apredetermined lower range of discharge pressures, and means associatedwith the last said means to subject the pressure responsive device toatmospheric zo pressure when the discharge pressure is outside pressureand means said predetermined range.-

8. A regulator for a motor driven uid compressor having a speed governorcomprising a pressure responsive device for controlling the speed of thegovernor in accordance with variations in the discharge pressure of thecompressor having a maximum speed setting position and a minimum speedsetting position, means to normally maintain the governor at a maximumspeed setting, means to unload the compressor at aV maximum dischargepressure and to reload the compressor at a predetermined low dischargepressure, means to render the pressure responsive device operative at apredetermined high pressure intermediate said maximum and W dischargepressures to cause the governor to adjust and maintain the motor speedat a minimum and to render the pressure responsive device inoperative-tocause the governor to accelerate the speed of the motor Ato' a maximumwhen a predetermined minimum rdischarge pressure less than said lowdischarge pressure is reached.

9. A regulator for a motor driven duid compressor having a governorcomprising a pressure responsive device actuated in accordance withvariations in the discharge pressure of the compressor normallypositioned to maintain the governor at the maximum speed setting andhaving a minimum speed setting position, means to unload the compressorat a predetermined maximum discharge pressor at a predetermined lowdischarge pressure, means responsive to a predetermined high dischargepressure intermediate said predetermined maximum and predetermined lovv-discharge pressures to render said pressure responsive device operativeto move to its minimum speedf setting position thereby changing thegovernor to its minimum speed setting.

l0. In a governor speed regulator for a motor driven uid compressor, apressure responsive device having maximum and minimum speed settingpositions for controlling the governor in accordance With variations inthe discharge pressure of the compressor, means to unload thecompressorat a predetermined maximum discharge to reload the compressorat a predetermined low discharge pressure, and means normallymaintaining the pressure responsive device in the maximuml speed settingposition' until a predetermined high pressure. intermediate saidpredetermined maximum and low ydischarge pressures is reached. i

11. In a governor speed regulator for a motor driven uid compressor, apressure responsive to reload the compressor at pressure and to reloadthe comdevice having a maximum speed setting position and a minimumspeed setting position for con- `trolling the governor in accordanceyvvith variations in the discharge pressure of the compressor, means tounload the compressor at a predetermined maximum discharge pressure andmeans to reload the compressor at a predetermined low dischargepressure, means responsive to the discharge pressure of the compressornormally preventing movement of the pressure responsive device from itsmaximum speed setting position to efiect movement of the pressureresponsivedevice to its minimum speed setting position when apredetermined high -pressure intermediate said predetermined maximum andpredetermined low discharge pressures is reached, and means topredetermine said high pressure.

l2. In a governor speed regulator for a motor driven uid compressorhaving a receiver tank, means to unload the compressor at apredetermined maximum discharge pressure and means a predetermined lowdischarge pressure, a casing containing a chamber, a piston in thechamber, a spring normally preventing movement of the piston, a seriesoi interconnected levers for transmittingmovement of the piston to thegovernor, a second'casing having a chamber communicating with thereceiver tank, a conduit connecting the two casings, a piston in thesecond chamber, a piston seat in the chamber, a spring normally holdingthe piston against the seat to prevent communication between thereceiver and the rst chamber, meansto adjust the tension on the springwhereby the piston in the second chamber may be moved from its seat by apredetermined high pressure intermediate said predetermined maximum andlow discharge pressures in the receiver to permit the pressure in thereceiver to move the piston in the first said chamber against thetension of its spring and to reseat upon occurrence of a predeterminedminimum pressure less than said predetermined low pressure in thereceiver, means to vent the nrst chamber through the second chamber whenits piston is seated, and means to prevent Aventing when the piston isunseated.

13. In a regulator for a motor driven iiuid compressor having a speed.governing means, compressor discharge pressure actuated control meansfor the speed governing means receiving iiuid discharged by thecompressor, means to unload and reload the compressor in accordance withvariations in the compressor discharge presy sure, and means to preventthe pressure actuated control means from receiving compressor dischargenuid until the compressor discharge uuid pressure rea-ches apredetermined pressure less than the compressor unloading pressure.

14. In a regulator for a motor driven :duid compressor having a speedvgovernor and a receiver'V tank comprising means to unload the compressorat a predetermined max' um discharge. pressure and to reload thecompressor at a predetermined low discharge pressure, and a pressureresponsive device having a maximum speed setting position and a minimumspeed` setting position comprisingr means deiining a chambercommunicating with-the receiver, a piston in the chamber, means totransmit movement of the piston to the governor, a spring to normallymaintain the piston in the maximum speed setting position, meansnormally preventing communication between the receiver and chamberadapted to permit communication when the pressure in the receiverreaches a` predetermined high pressure and '..ntilr 15..In a regulatorfor a motor driven iluid compressor having a governor and a receivertank including means to unload the compressor 'eating with the receiver,pressure responsive means in the chamber, means to transmit movement otthe premure responsive device to the governor, means to normallymaintainfthe pressure responsive device in its maximum speed settingposition, means normally preventing communication between the receiverand chamber adapted to permit communication within a predeterminedpreure mined high discharge pressure less than the predetermined maximumdischarge pressure has been reached. and means to predetermine said 1'ange.

ALLAN' O. CARPENTER.

range after a predeter-

